1) Field of the Invention
This invention relates to a method for producing a tin-nickel alloy film, particularly a method for producing a tin-nickel alloy film for decorative purposes.
2) Description of the Prior Art
Recently, attention has been paid to a tin-nickel alloy film to replace a decorative chromium plating film. Although the chromium plating film has some excellent properties such as wear-resistance and corrosion-resistance, it is strictly restricted in use because it has harmful element, Cr with respect to the environment. The use of the chromium plating film is expected to be more severely restricted in the future. Therefore, the tin-nickel alloy film would play very important roles in the future instead of the chromium plating film.
In the past, the tin-nickel film would be produced from a given water solution by alloy-electroplating, and thus, two different metals, tin and nickel, must be electroplated at the same voltage. Then, all kinds of things to perform the electroplating at the same voltage have been carried out. Moreover, chemical species to be used have been restricted, and anti-environmental additives have been used.
Furthermore, the above electroplated tin-nickel film from the water solution always has a non-equilibrium NiSn phase which is not recognized in its equilibrium diagram. The NiSn phase often shifts to another stable phase due to the wear or the heating in the use of the tin-nickel alloy film, and thus, the properties of the tin-nickel alloy film often change. Therefore, the functions given to the tin-nickel alloy film for predetermined purposes may change during the use of the film, so that it may be that the tin-nickel alloy film can not exhibit the predetermined functions.
In the above case, various modifications in electroplating condition and additives have been performed for preventing the occurrence of the unstable NiSn phase, but can not generate another stable phase except the unstable NiSn phase.
It is an object of the present invention to provide a method for producing a stable tin-nickel alloy film not including a non-equilibrium NiSn phase.
For achieving the above object, this invention relates to a method for producing a tin-nickel alloy film comprising the steps of:
depositing a tin layer and a nickel layer on a given substrate sequentially, thereby to form a multilayered film composed of the tin layer and the nickel layer, and
heating the multilayered film at a given temperature to form the tin-nickel alloy film.
The inventors have intensely studied to obtain the tin-nickel alloy film not including a non-equilibrium NiSn phase. As a result, they have found out a new method for producing the above tin-nickel alloy film in which films made of tin or nickel which is the component in the tin-nickel alloy film are stacked to form a multilayered film, and then, the multilayered film is heated to a given temperature to diffuse the tin elements and the nickel elements into the respective opposite layers, and thus, obtain the tin-nickel alloy film.
That is, according to the present invention, the tin-nickel alloy film is produced indirectly through the diffusion of the tin elements to constitute the tin-film and the nickel elements to constitute the nickel film.
Therefore, even though the non-equilibrium NiSn phase is generated, it is shifted to another stable NiSn phase in the heat-diffusion process of the present invention. As a result, since the thus obtained tin-nickel alloy film does not have the non-equilibrium NiSn phase, different from the above electroplated tin-nickel alloy film, it can maintain its original properties in use, and the original functions given to the tin-nickel alloy film can be maintained for a long time.